1. Field of the Invention
This invention relates to the automatic control of the current or voltage of an arc drawn between an electrode and a workpiece for purposes of air-carbon arc cutting and gouging.
2. Background Art
In air-carbon arc cutting and gouging of metal, it is highly desirable to be able to accurately control the spacing of an electrode with respect to a workpiece so as to effect an accurate cut. As described in U.S. Pat. No. 3,659,071, it has previously been possible to control the spacing of an electrode with respect to the workpiece to a close tolerance by sensing any variation in arc voltage from a steeply drooping voltage source. The electrode then would be automatically moved in a direction to cancel the variation.
Prior air-carbon arc metal removal systems have been limited in that they have not been compatible with both constant potential and constant current sources nor have they provided certain control and automation features. U.S. Pat. No. 4,320,282 shows control of arc sustaining parameters to mitigate arc quenching impulse noise.
Accordingly, an object of the present invention is a system for automatically controlling an arc which is powered from either a constant potential source or a constant current source.
Another object of the invention is automatically providing relative motion between the electrode and the workpiece after arc current above a predetermined value has been present a predetermined amount of time.
Another object is automatically turning the arc source off if the arc voltage drops below or rises above a predetermined threshold for a predetermined amount of time.
Still another object of the invention is automatically turning the arc source off if the arc current drops below a predetermined threshold for a predetermined amount of time.
A still further object is automatically retracting the electrode from the workpiece for a predetermined amount of time long enough to insure physical separation of the electrode and the workpiece when the arc current has been extinguished.